Nowadays, optical modules such as transmitter optical sub assembly (TOSA) and receiver optical sub assembly (ROSA) are widely used in information processing which is performed via optical communication or optical signal. Here, the TOSA is a miniature optical device with a light-emitting element (for example a laser diode) carried thereon for transmitting signal, and the ROSA is a miniature optical device having a light-receiving element (such as a photodiode) carried thereon for receiving signal. These optical modules are formed by bonding a can portion and a barrel portion together, the can portion being formed by encasing optical semiconductor elements such as light-emitting element or light-receiving element by a cover e.g. metal cover, the barrel portion being equipped with a lens.
In prior art, the can portion and the barrel portion are aligned with an optical semiconductor element disposed on the can portion and an optical axis of a lens disposed on the barrel portion, and bonded together by adhesive such as thermoset resin, e.g. epoxy resin. However, curing the resin takes a long time of heating; in addition, deterioration of work property and work efficiency, or resin deformation that occurs during curing process, may cause deflection of the optical axis. Resultantly, a method for solving the above problems is proposed, in which bonding is performed instantly using ultraviolet curing adhesive; however, ultraviolet curing adhesive has low adhesion intensity which may cause to form uncured region easily, and ultraviolet curing adhesive has low weather resistance. According to content documented in patent reference 1, a method is disclosed, in which thermoset resin is dispensed in form of spot and then heated to cure by high frequency induction heating, after that another type of thermoset resin is dispensed thereon and cured by heating in air.
In addition, according to content documented in patent reference 2, a method is described in consideration of the problem of higher temperature in local region caused by high frequency induction heating disclosed in patent reference 1. The method comprises a step of dispensing a curing resin, which is capable of receiving ultraviolet radiation and being heated, on a bonding surface of the can portion and the barrel portion, a step of temporary fixation by ultraviolet radiation and a step of reheating and curing the nonbonding region by irradiating ultraviolet after the center portion is aligned.
Patent reference 1: Japanese patent application publication NO. 2000-91642.
Patent reference 2: Japanese patent application publication NO. 2002-90587.
However, conventional technology described above has following problems. Firstly, as for an optical module, it is preferred that the optical module take a hermetic structure to improve reliability of the optical semiconductor element disposed on the can portion, thus preventing contact of the optical semiconductor with atmosphere especially contact with moisture, and avoiding degradation phenomena. However, heating of the resin in a hermetic environment results in thermal inflation of the gas contained in the barrel portion, in addition, as thermal inflation coefficient of the gas is greatly larger than that of material that forms the can portion and the barrel portion, the gas leaks through the bonding resin, and bubbles or fissures are formed in the bonding resin, thus causing problem of degraded sealability. Moreover, in normal case, resin with higher curing temperature presents better adhesion or sealability and can achieve high quality of bonding. However, heating at high temperature makes interior liquid expanding gradually, thus limiting usage of the high temperature resin, and affecting reliable and high quality of bonding. According to content of foregoing patent reference, since through holes are formed on the barrel portion, leakage of inflated gas is uneasy to happen; but these through hole need to be sealed by adhesive after the bonding process, and this further complicates the operation process and increases manufacture cost. Moreover, if these through hole are not sealed, the light-emitting element will be influenced by exterior environment and reliability thereof will be weakened.
When irradiating the curing resin using UV light, gas temperature in the barrel portion may still rise to a high level, thereby causing similar problem of thermal expansion.
When irradiation intensity of UV light is reduced for purpose of thermal expansion restriction, curing time will be prolonged and this will have influence on production in batch. Furthermore, since UV curing adhesive or curing resin for purpose of UV irradiation and heating is expensive, and UV irradiation device is necessary, the manufacture cost is increased greatly.